Measurement based on a micromechanical acceleration sensor has proven to be in principle a simple and reliable manner of measuring acceleration. In the case of a micromechanical acceleration sensor, measurement is based, for example, in the capacitance measurement on a change of a gap between two surfaces of a electrode pair of a sensor caused by acceleration. The capacitance between the surfaces, i.e. the storage capacity of the electrical charge, depends on the surface area of the surfaces and the distance between the surfaces. A measurement based on a micromechanical acceleration sensor such as a capacitance measurement can be used even with particularly small acceleration measurement areas.
Small-sized micromechanical acceleration sensors are often used in particularly critical application sites, such as, for example, in ABS and ESP systems (ABS, Antilocking Brake System; ESP, Electronic Stability Program) used in the automobile industry. For this reason, it is vitally important to assure the proper function of the capacitative acceleration sensors at start-up as well as in constant use. In demanding application sites there is a desire to know all deviations exceeding the device specifications in the functionality of the acceleration sensor after factory calibration. These types of deviations can be, among others, offset deviations, sensitivity deviations or physical damages.
Currently are known some micromechanical acceleration sensor solutions according to known art measuring in relation to several axes. For example, Finnish patent application publications FI 20030206 and FI 20030207 describe capacitative acceleration sensor solutions according to known art measuring in relation to several axes.
In acceleration sensor solutions according to known art, a disadvantage has been the observation of the functional reliability of the sensor at start-up as well as in constant use. In acceleration sensor solutions according to known art, a known self-testing arrangement can be used, in which the acceleration sensor is subjected to high voltage. The high voltage causes an electrostatic force between the measurement electrode and the mass of the sensor, resulting in bending of the spring and shifting of the mass, which changes the capacitance of the sensor, which can be measured using an ASIC (ASIC, Application Specific Integrated Circuit).
Using the self-testing arrangement described above offset deviations or sensitivity deviations due to time or temperature cannot be measured. Additionally, measurement of acceleration must be interrupted during self-testing.
In micromechanical acceleration sensor solutions according to known art and their self-testing methods, a disadvantage has also been the implementation of high voltage parts in the circuit structures used, which creates many disadvantages in the design and realization of circuit technology related to the acceleration sensor.
In demanding application sites of micromechanical acceleration sensors there is a clearly growing need for micromechanical acceleration sensors of greater functional reliability than earlier solutions, which are suitable for use in reliable measurement of acceleration particularly in small-sized micromechanical acceleration sensor solutions measuring in relation to several axes.